Buggy code:
public class ClientDataImportHandler extends AbstractDataImportHandler { private static final Logger logger = LoggerFactory . getLogger ( ClientDataImportHandler . class ) ; private static final int FIRST_NAME_COL = 0 ; private static final int FULL_NAME_COL = 0 ; private static final int LAST_NAME_COL = 1 ; private static final int MIDDLE_NAME_COL = 2 ; private static final int OFFICE_NAME_COL = 3 ; private static final int STAFF_NAME_COL = 4 ; private static final int EXTERNAL_ID_COL = 5 ; private static final int ACTIVATION_DATE_COL = 6 ; private static final int ACTIVE_COL = 7 ; private static final int MOBILE_NO_COL = 8 ; private static final int DOB_COL = 9 ; private static final int GENDER_COL = 10 ; private static final int STATUS_COL = 11 ; private List < Client > clients ; private String clientType ; private final RestClient restClient ; private final Workbook workbook ; public ClientDataImportHandler ( Workbook workbook , RestClient client ) { } @ Override public Result parse ( ) { } private String getClientType ( Sheet clientSheet ) { } private Client parseAsClient ( Row row ) { String officeName = readAsString ( ClientDataImportHandler . OFFICE_NAME_COL , row ) ; String officeId = getIdByName ( workbook . getSheet ( "Offices" ) , officeName ) . toString ( ) ; String staffName = readAsString ( ClientDataImportHandler . STAFF_NAME_COL , row ) ; String staffId = getIdByName ( workbook . getSheet ( "Staff" ) , staffName ) . toString ( ) ; String externalId = readAsString ( ClientDataImportHandler . EXTERNAL_ID_COL , row ) ; String activationDate = readAsDate ( ClientDataImportHandler . ACTIVATION_DATE_COL , row ) ; String active = readAsBoolean ( ClientDataImportHandler . ACTIVE_COL , row ) . toString ( ) ; String dateOfBirth = readAsDate ( ClientDataImportHandler . DOB_COL , row ) ; <START_BUG> String mobileNo = readAsBoolean ( ClientDataImportHandler . MOBILE_NO_COL , row ) . toString ( ) ; <END_BUG> if ( clientType . equals ( "Individual" ) ) { String firstName = readAsString ( ClientDataImportHandler . FIRST_NAME_COL , row ) ; String lastName = readAsString ( ClientDataImportHandler . LAST_NAME_COL , row ) ; String middleName = readAsString ( ClientDataImportHandler . MIDDLE_NAME_COL , row ) ; String gender = readAsString ( ClientDataImportHandler . GENDER_COL , row ) ; String genderId = null ; if ( ! ( gender . equals ( "" ) ) ) { genderId = getIdByName ( workbook . getSheet ( "Extras" ) , gender ) . toString ( ) ; } if ( StringUtils . isBlank ( firstName ) ) { throw new IllegalArgumentException ( "Name<seq2seq4repair_space>is<seq2seq4repair_space>blank" ) ; } return new Client ( firstName , lastName , middleName , activationDate , active , externalId , officeId , staffId , mobileNo , dateOfBirth , genderId , row . getRowNum ( ) ) ; } else { String fullName = readAsString ( ClientDataImportHandler . FULL_NAME_COL , row ) ; if ( StringUtils . isBlank ( fullName ) ) { throw new IllegalArgumentException ( "Name<seq2seq4repair_space>is<seq2seq4repair_space>blank" ) ; } return new org . openmf . mifos . dataimport . dto . client . CorporateClient ( fullName , activationDate , active , externalId , officeId , staffId , mobileNo , row . getRowNum ( ) ) ; } } @ Override public Result upload ( ) { } public List < Client > getClients ( ) { } }

Fix:
String mobileNo = readAsString ( ClientDataImportHandler . MOBILE_NO_COL , row ) . toString ( ) ;